Pick and place tools, which may be in the form of vacuum collets or suction heads, are used in automated semiconductor manufacturing processes to transfer electronic components or materials from one location to another. One such application of a pick and place tool is in the transfer of semiconductor dice from a cut semiconductor wafer to a bond pad of a substrate during a packaging process.
Typically, an adhesive material is placed onto the substrate for bonding the semiconductor die to the bond pad. The adhesive material may be in liquid form, such as epoxy, or in tape form, such as a polyimide tape, as disclosed in US Patent Publication number 2002/0109217 in respect of an “Apparatus for Die Bonding”. An advantage of using adhesive tape is that it is electrically insulating and it does not overspread on the bond pad during attachment of a die onto it. Overspreading may lead to defects during later processing of the component.
Another application of adhesive material is in the fabrication of a stacked die CSP (“Chip-Scale Package”). Stacked die CSPs serve to increase the semiconductor die density of a semiconductor package by including two or more semiconductor dice in one package. A high density package, having multiple semiconductor dice therein, increases the electronic component density on a printed circuit board. Such a high density semiconductor package also maximizes space utilization on a printed circuit board and further increases the number of active elements on the printed circuit board. Liquid adhesive is not desirable as an adhesive material for stacking the dice due to the aforesaid problem of overspreading, and adhesive tape or film is generally preferred. Therefore, the application of thin adhesive films or thermoplastic adhesive films is one of the major processes involved in the assembly and packaging of semiconductor devices, especially those involving stacked die CSPs.
Pick and place tools usually consist of flat or recessed vacuum collets or suction heads. Hard materials or materials with some resilience like rubber are used in contact surfaces for these suction heads for compliance with the surface of a material picked. When such pick and place tools are used to pick a thin thermoplastic adhesive film and to place it onto a flat heated substrate for bonding, air bubbles may be trapped and form voids between the interface of the adhesive film and the substrate and/or die. Even if the surface of a pick and place tool is perfectly flat, these voids may be unavoidable. Amongst other things, this is due to the flexible nature of the film material and difficulty in tensioning the film since the film is held by vacuum suction only. As a result, such voids may cause defects in the fabrication of semiconductor devices.